The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
CBCoordinated BeamformingCDMCode Division MultiplexingC/ICarrier-to-Interference Power RatioCoMPCoordinated Multi-pointCQIChannel Quality IndicatorCSCoordinated SchedulingCSIChannel State InformationDCSDynamic Cell SelectionDLDownlinkDPSDynamic Point SelectionE-UTRAEvolved Universal Terrestrial Radio AccesseNBEvolved Node B/Base Station in an E-UTRAN SystemE-UTRANEvolved UTRAN (LTE)FDMFrequency Division MultiplexingITUInternational Telecommunication UnionJTJoint TransmissionLOSLine-of-sightLTELong Term EvolutionLTE-ALong Term Evolution AdvancedMIMOMultiple Input Multiple OutputPRBPhysical Resource BlockPDCCHPhysical Downlink Control ChannelPDSCHPhysical Downlink Shared ChannelPMIPrecoding Matrix IndexPUCCHPhysical Uplink Control ChannelPUSCHPhysical Uplink Shared ChannelRBResource BlockRIRank IndexRANRadio Access NetworkRxReception, ReceiverSNRSignal-to-Noise RatioSRSsounding reference signalTDMTime Division MultiplexingTxTransmission, TransmitterUEUser EquipmentULUplinkUTRANUniversal Terrestrial Radio Access Network
Coordinated Multi-Point (CoMP) transmission is currently being investigated in 3GPP RAN documents, e.g., see R1-111637 (“System Performance of JP-CoMP in Homogeneous Networks with RRHs”, 3GPP TSG RAN WG1 Meeting #65, Barcelona, Spain, May 9-13, 2011), and R1-111600 (“Further Phase-1 Evaluation of Joint Transmission and DCS Schemes”, 3GPP TSG RAN WG1 Meeting #65, Barcelona, Spain, May 9-13, 2011).
The motivation for downlink (DL) CoMP is to allow fast coordination among different transmission points to improve a throughput performance. To enable closed-loop transmission from multiple transmission points to a given UE, channel state information for multiple radio links needs to be measured by the UE and sent to the network using the uplink control channel (PUCCH) or the uplink data channel (PUSCH). To simplify presentation a UE and two eNBs are considered, as shown in FIG. 1.
The UE communicates with eNB1 through a radio link A using uplink channels PUCCH and PUSCH and downlink channel PDCCH. In the case of the CoMP transmission the UE can receive a joint transmission using PDSCH from eNB1 through the link A and from eNB2 through a link B.
Each of these links may contain multiple transmit/multiple receive antennas and for simplicity it is assumed the UE has 2 receive antennas, and eNB1 and eNB2 having NTA, NTB transmit antennas. Then the radio links A and B define NTA×2 and NTB×2 channels, respectively. In addition to these links we can also consider a multi-point link from the eNB1 and eNB2 to UE as shown in FIG. 2 and further discussed below. The link AB may create (NTA+NTB)×2 channels.
In a CoMP scenario the UE can perform channel state information (CSI) measurements for the links A, B, AB and send the measurements to the eNB1 via the PUCCH or PUSCH. The measurement and signaling needed for serving cell CSI feedback (e.g., link A in FIG. 1) already exist in RANI specifications referenced above. This includes Precoding Matrix Index (PMI)/Channel Quality Indicator (CQI)/Rank Index (RI) feedback for codebook based precoding and CQI feedback for SRS based precoding. The PMI indicates an index out of a codebook of transmit matrices which the eNB should use to transmit to the UE, the CQI provides information for the eNB to determine the best modulation and coding rate for the UE, and the RI is an indication of the number of data streams (i.e., a rank) that the UE can support.
Coordinated scheduling and beamforming (CS/CB) and dynamic point selection (DPS) are CoMP techniques where the PDSCH transmission for a UE specific resource block (RB) is from one transmission point. Therefore CS/CB and DPS techniques are agnostic to spatial channel information between two or more transmission points. In such cases a natural extension of the serving cell CSI feedback mechanism is possible where a single cell CSI feedback can be supported for non-serving cells (e.g. the link B in this example).
Two approaches have been recently proposed for implementing the CoMP transmission.
The first approach involves Hierarchical PMI feedback (R1-111637, “System Performance of JP-CoMP in Homogeneous Networks with RRHs”, 3GPP TSG RAN WG1 Meeting #65, Barcelona, Spain, May 9-13, 2011). This technique has been proposed by multiple companies where an inter-point codebook (essentially a quantized phase difference between the eNB1 and eNB2) has been used. This implies that a PMI for the radio link A can be combined with a PMI for the radio link B by an inter-point codebook to generate a PMI for the multi-point radio link AB. It is however not clear whether and how the design handles ranks greater than one and whether orthonormality is guaranteed for rank-2 and higher disparate precoders for the link AB.
The second approach involves Non-Hierarchical PMI feedback (R1-111600, “Further Phase-1 Evaluation of Joint Transmission and DCS Schemes”, 3GPP TSG RAN WG1 Meeting #65, Barcelona, Spain, May 9-13, 2011). In this approach a single joint PMI is used for multi-point radio link AB in addition to a single cell PMI for radio link A. The advantage here is that the ranks can be different for the radio links A and AB and there is compression of PMI information by using a joint PMI. This approach, however, is not easily scalable to an increase in the number of transmission points and is not flexible in handling different numbers of transmit antennas for different transmission points.
Joint transmission (JT) is a CoMP technique where multiple transmission points transmit a UE specific RB on the PDSCH. Therefore JT requires knowledge of spatial information between transmission points. This means that cell CSI feedback methods do not naturally extend to the case of JT where spatial information is needed for the link AB shown in FIG. 2. Therefore there is a need to define simple feedback strategies for multi-point spatial channel information feedback.